I'm so sorry to hear this. :( I was so excited when I saw your other post and now I'm devastated.
I'm just glad you got him "home" in time so he can be happy and loved during his last days. You know he appreciates it by how he's purring for you - what a sweetie. :(
And don't worry about keeping him in the spare room. I'm sure it's 1000 times better than at the shelter. He's got plenty of room, the right food and lots of love.
You two are just so great for providing him with all this knowing he had problems and wasn't the healthiest cat around.
Enjoy your new home Bob, for as long as you are able. You certainly deserve it.